ON/OFF
V
V
20
®
2
200m
200m
A
200m
20m
20A
200µ
2m
20m
20A
2m
200µ
200k
200m
A
Typical Problems:
HOLD
750 200
1000
200
20
2
20M
2M
200k
Ω
20k
2k
DUTY
%
20k 2k 200
Hz
85XT
VΩ
CAT
II
MAX
1000V
750V
COM
mA
How-to Test it Yourself
20A
200mA MAX
FUSED
MAX
20A/30sec
FUSED
figure 7
wires to expose clean metal, reseating the connectors, and
securely tightening all screws or nuts. Any wiring or
switches that show a high voltage drop should be replaced.
Automotive
Electrical
Most automotive electrical problems can be traced to a bad
connection or a failed component. High resistance ground connections can be one of the most frustrating of electrical problems.
They can produce bizarre symptoms that don't seem to have anything to do with the cause, once you finally find it. The symptoms
include lights that glow dimly, lights that come on when others
should, gauges that change when the headlights are turned on, or
lights that don't come on at all. A failed alternator, a bad battery,
or a blown fuse can all result in things just not working at all.
6. Testing Switch Operation:
Task Summary:
Use the resistance of connectivity function to find a bad
switch. With power removed from the circuit, set your
meter to measure resistance or continuity and probe
sides of the switch. Operate the switch and watch for a
change on the meter display. If the display doesn’t
change, the switch is defective. (see figure 2)
This booklet will help you diagnose and fix common electrical
problems in your car. When troubleshooting electrical systems,
it's important to use a logical process of deductive reasoning to
solve the problem. This process is most important since, unlike
mechanical devices, you can't see inside or dismantle the majority
of electrical components to tell whether they're functioning.
We’ll start with the battery and charging circuit, then look at bad
grounds and other electrical connections, then finish by checking
for failed components.
If not, it may be time to replace the component completely. If you suspect a more serious problem, call a
qualified certified automotive technician for help.
7. Where to Go From Here:
With the help of the tips and techniques in this booklet,
you should be able to troubleshoot most of the common
electrical problems. When troubleshooting automotive
electrical systems, it’s important to use a logical process
of deductive reasoning to solve the problem. Jumping to
conclusions can be expensive and time consuming.
Just use this simple approach: check for power, check
fuses and switches, check connections, and check for
good grounds.
Recommended Tools:
®
You will need a DMM that measures dc volts, ac volts, resistance,
and continuity. You will also need a current clamp accessory that
measures dc current. As an alternative, use a clamp-on multimeter
that combines all the above measurement capabilities. It is
assumed you have basic knowledge of how to make electrical
measurements and how to operate a DMM or clamp meter. If not,
you should start by reading “Basic DMM Measurements” and your
DMM or clamp meter owner’s manual.
Meterman.
The right tool for the job.™
Meterman Test Tools
website: www.metermantesttools.com
email: info@metermantesttools.com
6920 Seaway Blvd.
Everett, WA 98203
fax: 425-446-4882
tel: 877-596-2680
Meterman Test Tools Europe
P.O. Box 1186
5602 BD Eindhoven
The Netherlands
1643507 B-ENG-N Rev. A
Auto #11
FPO
ON/OFF
Step by step
troubleshooting:
V
ON/OFF
ON/OFF
V
750 200
1000
200
20
V
20
2
200m
2
200m
A
2. Verifying a Good Alternator:
To perform this test, the battery must
be fully charged (see step 1). Run the
engine at idle and verify that no-load
voltage is 13.8 - 15.3. volts dc (check
ON/OFF
HOLD
20m
20A
2m
20m
20A
2m
2m
20m
20A
2m
200µ
V
20
2
200m
2
20M
2M
200k
Ω
DUTY
%
20k 2k 200
VΩ
CAT
II
MAX
1000V
750V
COM
mA
A
20k
2k
DUTY
%
20k 2k 200
Hz
Ω
VΩ
CAT
II
MAX
1000V
750V
20A
COM
mA
VΩ
20A
200mA MAX
FUSED
MAX
1000V
750V
MAX
20A/30sec
FUSED
COM
mA
CAT
II
COM
mA
Test
MAX
1000V
750V
CAT
II
MAX
1000V
750V
20k 2k 200
Hz
COM
mA
20A
200mA MAX
FUSED
MAX
20A/30sec
FUSED
Test
200mA MAX
FUSED
MAX
20A/30sec
FUSED
Electricity can be
dangerous. Protect
yourself and your car
by remembering to
follow a few simple
rules when working
with electrical circuits:
600V
200mA MAX
FUSED
MAX
20A/30sec
FUSED
CAT
III
II
Test
LD
HO
AC
DC
Test
Ω
V
OF
F
A
Test
Solenoid
40A
AC
600V X
T III MA
CA
400A 0V X
60
MA
Work
safely!
20A
200mA MAX
FUSED
MAX
20A/30sec
FUSED
20k
2k
DUTY
%
85XT
VΩ
Hz
20A
VΩ
Ω
20k
2k
DUTY
%
20k 2k 200
85XT
CAT
II
20M
2M
200k
200µ
Ω
A
2m
200µ
200k
200m
A
200k
20M
2M
200k
85XT
85XT
Hz
A
Hz
A
200m
20m
20A
2m
2m
20m
20A
200m
20k
2k
DUTY
%
20k 2k 200
200m
20m
20A
2m
20m
20A
2
200µ
200µ
20M
2M
200k
20
200m
200µ
V
200m
200k
200m
200k
200m
750 200
1000
200
20
2
200m
200µ
200µ
20k
2k
A
20m
20A
200k
20M
2M
200k
200m
200m
200m
V
2
2
A
V
20
200µ
A
200m
20m
20A
2m
200µ
If your battery becomes discharged it
will be unable to provide sufficient
voltage or current to the starter, hence
the engine won't crank. The first step
is to test the battery and charge it if
necessary.
Percent Charge
100%
75%
50%
25%
HOLD
750 200
1000
200
20
HOLD
750 200
1000
200
20
2
200m
HOLD
2m
20m
20A
200m
1. Measuring Battery Voltage:
Voltage
12.60V to 12.72V
12.45V
12.30V
12.15V
V
200m
85XT
Readings obtained at 80°F (27°C)
ON/OFF
V
20
20
Ω
No-Load Test
750 200
1000
200
2
A
Verify that the connections to the battery look clean and are tight. With the
engine off, bleed the surface charge
from the battery by turning on the
headlights for a minute. Now with the
lights off, set your DMM to the dc voltage function, 20 volt range, and measure the voltage across the battery terminals by touching the red probe tip
to the “+” terminal and the black
probe tip to the “-” terminal. Use the
chart below to determine the approximate percent charge on the battery. If
the battery voltage reads low, the battery may be damaged or worn out, or
the charging system is not working correctly. See below for how to verify the
alternator is working. A more complete
load test should be done to indicate
battery performance under load and
determine if the battery is damaged.
HOLD
200m
V
+
M
CO
figure 2
figure 1
figure 3
figure 4
figure 5
Test
figure 6
Diagnosing common automotive electrical problems
as in step 1). Next, load the alternator
to rated output current by turning on
as many accessories as possible (e.g.
headlights, brake lights, heater fan,
rear window defogger and lighter).
Run the engine at a fast idle, about
2000 RPM. Check the output current of
the alternator with a dc current clamp
(see Figure 2) to see if it is at or near
the rated output current. Now check
the alternator output voltage. (see
Figure 3) The alternator must maintain at least 12.6 volts dc output at
rated alternator current output.
3. Checking Ripple Voltage:
The alternator generates ac voltage
which is converted to dc voltage. The
output of a properly functioning alternator will show a small amount of ac
voltage called "ripple". A good alternator should measure less than 0.5 volts
ac ripple with the engine running and
loads applied.
Run the engine at fast idle and turn on
accessories to load the alternator.
Measure the ripple voltage by switching your DMM to the ac volts function,
2 volt range, and connecting the black
lead to a good ground (such as the
engine block) and the red lead to the
“BAT” terminal on the back of the alternator (not at the battery). (see figure 4)
A reading higher than 0.5 volts ac may
indicate damaged alternator diodes.
To rule out the wiring as the source of
the trouble, check all the wire connections between the alternator and the
battery terminals. Refer to Step 5,
“Testing for Bad Connections” for
details on performing a voltage drop
test. A resulting voltage drop of
200 mV or greater requires that the
wiring connectors need cleaning and
tightening, or replacement.
If the wiring is OK, have the engine’s
charging circuit serviced.
4. Testing for Circuit Integrity:
Electrical devices need good, solid
connections in order to operate properly. This is particularly true in automobiles since the power source is a
battery. Vibration, temperature
extremes, and corrosion from salt and
rain can cause good connections to go
bad in your car. Loose connectors,
build-up of rust and corrosion, broken
wires, and damaged switches are all
examples of bad connections.
If a device is not working properly,
first check to make sure it is getting
power. Set your DMM to the dc voltage function, 20 volt range. Connect
the black lead to a good ground and
probe with the red lead on the “+”
input of the device. (Make sure the
ignition switch is turned ON. Many
accessories do not operate with the
ignition turned off.) If the reading is
zero, there is no power to the device.
This could be an indication of a
blown fuse.
To check for a blown fuse, first locate
the fuse holder. This is usually a block
about the size of a pack of cigarettes
with a plastic cover located either
under the dashboard or in the engine
compartment. Remove the cover. Use
the diagram on the cover to locate
the fuse that supplies power to the
accessory or device you are testing.
(see figure 5)
To test the fuse, set the DMM to
the dc voltage function and connect
the black lead to a good ground, then
probe both sides of the fuse for
12 volts dc. A good fuse will show
12 volts on both sides. A blown fuse
will show 12 volts on one side only.
If you cannot easily probe both sides
of the fuse, as an alternative you can
remove the fuse and check it for continuity. Set the DMM to the continuity
function and probe one side with the
black lead and the other side with the
red lead. A good fuse will sound the
continuity beeper and show almost
zero ohms of resistance. A bad fuse
will not sound the beeper and will
show “OL” for resistance. Replace any
blown fuse only with one of the same
type and current rating.
5. Testing for Bad Connections:
A bad, or high resistance, ground
connection robs some of the voltage
needed by the device you want to
run. If a device is not operating properly, check all the connections leading
up to the device, and back to the battery. Suspect connections include terminal posts, crimp connectors, bulb
sockets, switches, and even the
wiring itself. (see figure 6)
To check for a bad connection, you
need to measure the voltage drop
across the connection. The higher the
voltage drop, the worse the connection. Current must be flowing for the
meter to register the voltage drop
found. Turn ON the device (and the
ignition, if necessary). Set your multimeter to the dc voltage function,
3 volt range. Connect the red lead to
the side of the connection nearer the
battery positive (+) terminal and the
black lead to the side nearer the battery negative (-) terminal or ground.
The measured voltage drop should
not exceed the following:
300 mV (0.3 V)
200 mV (0.2 V)
100 mV (0.1 V)
0 mV to <50 mV
0.0 V
Switch
Wire or cable
Ground
Sensor
Connections
Connections
If you find a higher voltage reading
you have a bad connection. Try cleaning the contacts by removing any rust
or corrosion, scraping the metal or
(continued on back)
• Make sure your meter is
working with a 3-point
check: Measure a known
live circuit, next measure the circuit you’re
working on and finally
re-check the known live
circuit.
• Only use a meter that
has the proper voltage
ranges for the job at
hand and make sure
the meter has the
proper safety ratings
and protection.
• Use caution when
reaching inside the
engine compartment.
Parts of the engine may
be very hot, and the fan
may start automatically
• Don’t wear loose
fitting clothing,
jewelry or a tie that
can become caught in
moving pulleys and
belts. Make sure test
leads are safely out of
the way of all moving
parts of the engine.